Solder-bearing contacts and method of manufacture thereof and use in connectors

ABSTRACT

In one aspect, a surface mount contact is provided for attachment to a circuit board or the like. The contact includes an elongated electrically conductive pin that has a first end and an opposing second end. A pre-formed heat re-flowable material is attached to one end of the pin and a conductive locator member surrounds the pin at a location between the first and second ends thereof and adjacent the conductive locator member. In one embodiment, the locator member is in the form of a cylindrical collar that extends around the pin.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 10/922,789 which claims the benefit of U.S. patent applicationSer. No. 60/499,811, filed Sep. 2, 2003, each of which is herebyincorporated by reference in its entirety.

TECHNICAL FIELD

The present invention relates to the field of devices for joiningelectrical components to one another and, more particularly, to anapparatus for facilitating the soldering of a first electronic device,such as a printed circuit board or connector, to a second electronicdevice, such as a printed circuit board and to a method of forming asolder ball on a contact.

BACKGROUND

It is often necessary and desirable to electrically connect onecomponent to another component. For example, a multi-terminal component,such as a connector, is often electrically connected to a substrate,such as a printed circuit board, so that the contacts or terminals ofthe component are securely attached to contact pads formed on thesubstrate and/or to holes lined with an electroplating material in thesubstrate to provide an electrical connection therebetween. Onepreferred technique for securely attaching the component terminals tothe contact pads and/or plated lining holes is to use a solder material.

When joining a multi-terminal component, such as a connector, to asubstrate by soldering, particularly a substrate with internally platedholes, special provisions have often been required, such as shown inU.S. Pat. Nos. 4,597,625; 4,802,862; 4,883,435; 5,139,448; and5,334,059, all of which are incorporated herein by reference in theirentirety. Such components have terminals which do not carry solder, sothat these situations have generally required special means forproviding solder to the component terminals and to contact pads on thesubstrate. One approach to providing solder to the component terminalsand contact pads is to provide solder paste in and around the particulararea, such a hole. However, this approach generally does not provide asufficient volume of solder to properly join the component terminals andcontact pads.

In the mounting of an integrated circuit (IC) on a substrate (e.g.,formed of a plastic or a ceramic), the use of ball grid array (BGA) orother similar packages has become common. In a typical BGA, sphericalsolder balls attached to the IC package are positioned on electricalcontact pads of a circuit substrate to which a layer of solder paste hasbeen applied. The solder paste is applied using any number oftechniques, including the use of a screen or mask. The unit is thenheated to a temperature at which the solder paste and at least a portionor all of the solder balls melt and fuse to an underlying conductive padformed on the circuit substrate. The IC is thereby connected to thesubstrate without need of external leads on the IC.

The BGA concept also offers significant advantages in speed, density,and reliability and as a result, the BGA package has become thepackaging option of choice for high performance semiconductors. Theinherent low profile and area array configuration provide the speed anddensity and the solid solder spheres provide enhanced solder jointreliability. Reliability is enhanced because the solder joints occur ona spheroid shape of solid solder. The spheroid shape, when properlyfilleted, provides more strength than flat or rectangular shaped leadsof equivalent area. The solid solder composition provides a morereliable solder joint than conventional stamped and plated leads becausethere can be no nickel underplate or base metal migration to contaminateor oxidize the solderable surface, or weak intermetallic layers than canform when the solder bonds to a nickel underplate. Further, tin and tinplating processes used on conventional stamped and plated leads haveadditives than can inhibit solderability. Enhanced solder jointreliability is particularly important to an area array package becausethe solder joints cannot be visually inspected.

While the use of a BGA connector in connecting the IC to the substratehas many advantages, there are several disadvantages and limitations ofsuch devices. It is important for most situations that thesubstrate-engaging surfaces of the solder balls are coplanar to form asubstantially flat mounting interface so that in the final application,the solder balls will reflow and solder evenly to the planar printedcircuit board substrate. If there are any significant differences insolder coplanarity on a given substrate, this can cause poor solderingperformance when the connector is reflowed onto a printed circuit board.In order to achieve high soldering coplanarity, very tight coplanarityrequirements are necessary. The coplanarity of the solder balls isinfluenced by the size of the solder balls and their positioning on theconnector.

Conventional BGA connector designs attach loose solder balls to theassembled connector. The attachment process requires some type of ballplacement equipment to place solder balls on a contact pad or recessedarea of the connector that has been applied with a tacky flux or solderpaste. The connector then goes through a reflow oven to solder the ballsto the contact. The process is slow, sensitive, and requires expensive,specialized equipment.

An example of a BGA type connector is described in U.S. Pat. No.6,079,991, ('991) to Lemke et al., which is herein incorporated byreference in its entirety. The connector includes a base section havinga number of outer recesses formed on an outer surface of the basesection. Similarly, the base section also has a number of inner recessesformed on an inner surface of the base section. The inner recesses aredesigned to receive contacts and the outer recesses are designed toreceive solder balls so that the solder balls are fused to bottomsections of the contacts which extend into the outer recesses. Thecontacts comprise both ground/power contacts and signal contacts withtop sections of the contacts providing an electrical connection with anelectronic device by known techniques. Another electronic device, e.g.,a PCB, is electrically connected to the contacts by soldering the solderballs onto contacts formed on the PCB, thereby providing an electricalconnection between the two electronic devices.

While the '991 connector is suitable for use in some applications, itsuffers from several disadvantages. First, the connections between thesolder balls and the bottom sections of the contacts may lack robustnessand durability since the solder balls are simply placed in the outerrecesses and then reflowed to form the electrical connection between thecontact and one electronic device. Accordingly, only a portion of eachsolder ball is in contact with the bottom section of one contact beforeand after the soldering process. Second, because the solder balls aresimply inserted into the outer recesses, the solder balls may not becoplanar with one another during the use of the connector and during thereflow process. Another disadvantage of this type of connector is thatthe solder joints are especially susceptible to fracturing duringthermal expansion and cooling. The base section and the printed circuitboard typically each has a different coefficient of thermal expansionand therefore when both are heated, one component will expand greaterthan the other. This may result in the solder joint fracturing becausethe solder ball is confined within the outer recess and the movement ofthe end of the contact to which the solder ball is attached is limiteddue to housing constraints. In other words, the contact is held in placewithin the housing substrate and only slightly protrudes into the recesswhere the solder ball is disposed. The contact therefore is effectivelyheld rigid and not permitted to move during the reflow process.

In addition, the costs associated with manufacturing the '991 connectorare especially high since the contacts must be placed in the basesection and then the individual solder balls must be placed within theouter recesses formed in the base section. A BGA type connector likelyincludes hundreds of solder balls and thus, the process of insertingindividual solder balls into the outer recesses requires a considerableamount of time and is quite costly.

Another type of solder ball contact is disclosed in U.S. Pat. No.6,700,079. In the '079 patent, a surface mount contact for attachment toa circuit board is provided and includes an elongate electricallyconductive pin defining a shaft having an upper end and a lower end. Apre-formed heat re-flowable material, such as a solder ball, is attachedto the lower end of the pin and an insulator, such as a collar,surrounds the pin intermediate the upper and lower ends and is adjacentthe pre-formed heat re-flowable material. While this device may havesome particular utility, there are a number of disadvantages associatedtherewith. More specifically, the upper end of the pin is typicallyinserted into and secured within an opening in the upper PCB, while thepre-formed heat re-flowable material is reflowed to cause a connectionwith a second component, such as another printed circuit board. Theinsulator acts as a stop and is disposed adjacent the upper PCB. As onewill appreciate, an insulator does not attract heat and therefore, heatremains trapped between the insulator and the upper PCB and this canlead to a build up in heat in this interface region. In other words,heat can be trapped by the insulator and this can cause damage to theupper PCB since many components thereof are heat sensitive and thus areadversely affected by a heat buildup.

It is therefore desirable to provide an alternate surface mount contactfor attachment to a circuit board or a connector which overcomes theabove noted deficiencies.

SUMMARY

In one aspect, a surface mount contact is provided for attachment to acircuit board or the like. The contact includes an elongatedelectrically conductive pin that has a first end and an opposing secondend. A pre-formed heat re-flowable material is attached to one end ofthe pin and a conductive locator member surrounds the pin at a locationbetween the first and second ends thereof and adjacent the conductivelocator member. In one embodiment, the locator member is in the form ofa cylindrical collar that extends around the pin.

The locator member acts as a stop or locator since it abuts one face ofan electronic device when the contact is securely connected to theelectronic device. By being formed of a thermally dissipative,conductive material, the locator member serves to prevent orsubstantially reduce the likelihood that heat can become trappedunderneath the locator member at the interface between the locatormember and the electronic device. Trapped heat can lead to damage to theelectronic device or malfunction thereof.

In another aspect, one of the faces of the locator member is modified tofacilitate the formation of a solder ball at one end of the contact.More specifically, a process is provided whereby a mass of molten soldermaterial is introduced to the modified face and the face profile causesthe molten solder material to form a solder ball about the contact pin.In other words, one end of the contact pin is embedded in the solderball. This process thus eliminates the step of having to first pre-formand then attach the solder ball to the contact pin.

Other features and advantages of the present invention will be apparentfrom the following detailed description when read in conjunction withthe accompanying drawings.

BRIEF DESCRIPTION OF THE FIGURES

The foregoing and other features of the present invention will be morereadily apparent from the following detailed description and drawingsfigures of illustrative embodiments of the invention in which:

FIG. 1 is a perspective view, in partial cross-section, of a surfacemount contact with a heat re-flowable material being coupled to one endof an electrically conductive pin;

FIG. 2 is a perspective view of one exemplary locator member that formsa part of the contact of FIG. 1;

FIG. 3 is a cross-sectional view of a circuit board assembly includingthe contact of FIG. 1 subsequent to re-flow of the heat re-flowablematerial associated with the contact;

FIG. 4 is perspective view, partially in cross-section, of a surfacemount contact according to another embodiment;

FIG. 5 is a perspective view, partially in cross-section, of a surfacemount contact according to yet another embodiment;

FIGS. 6 and 7 are perspective views that illustrate cylindrical andsquare washer-like pre-formed heat re-flowable members that can be usedin place of the solder ball shown in FIG. 1;

FIG. 8 is a perspective view, in partial cross-section, of a locatormember according to another embodiment and having a recessed portionformed in a surface thereof;

FIG. 9 is perspective view, in partial cross-section, of a surface mountcontact including the locator member of FIG. 8 and a substrate of heatre-flowable material; and

FIG. 10 is a perspective view of the contact of FIG. 9 illustratingsolder ball formed by applying heat to the substrate of material.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIGS. 1 and 2 illustrate a surface mount contact 10 according to a firstembodiment and for attachment to a planar circuit board 50 (FIG. 3). Thecontact 10 includes an elongated electrically conductive pin 20 that hasa first end 22 and an opposing second end 24. Typically, the pin 20 isformed of a metal. The pin 20 can come in any number of different shapesand sizes and for purposes of illustration only, the illustrated pin 20has a relatively square cross-section; however, it can easily have acircular or oval cross-section. The first end 22 of the pin 20 can beslightly tapered, rounded, etc. to facilitate the retaining of a heatre-flowable material, generally indicated at 30, as will be describedbelow.

The contact 10 also includes a locator member 40 that surrounds aportion of the pin 20 and more specifically and according to oneexemplary, the locator member 40 is a collar member that surrounds theshaft of the pin 20 at a location between the first and second ends 22,24. In one exemplary embodiment and as illustrated in FIG. 2, thelocator member 40 is in the form of a cylindrical collar that has anopening 42 that is complementary to the shape of the pin 20 so that thepin 20 can extend therethrough, resulting in the locator member 40 beingdisposed around an intermediate portion of the shaft with a small spacebetween the pin 20 and the wall of the locator member 40. Theillustrated opening 42 has a similar or the same cross-sectional shapeas the pin 20 and consequently, the opening 42 has a square shape. Itwill clearly be understood that the square shape is merely exemplary innature; however, it will be understood that other shapes are suitable.

In contrast to conventional constructions, the locator member 40 isformed of a conductive material as opposed to an insulator material. Inone exemplary embodiment, the locator member 40 is formed of a materialthat is conductive and thermally dissipative as well as being nonwettable relative to a solder material or the like. One type of materialthat has these characteristics is a metal and more particularly, thelocator member 40 can be formed of aluminum or steel. By forming thelocator member 40 out of a material that offers these characteristics, anumber of advantages can be realized as described below.

When the contact 10 is prepared for use, the heat re-flowable material30, e.g., solder, is coupled to the pin 20 by embedding or otherwisedisposing the material 30 around the first end 22 of the pin 20. Forexample, the material 30 can be pre-formed to assume a distinct shape,such as a solder ball, and is then coupled to the first end 22 byembedding the pin 20 into the material 30 so that the material 30 issecurely held on the first end 22 as shown in FIG. 1.

The pin 20 and the locator member 40 can be formed using conventionalstamping techniques since these elements are formed of metal andtherefore are susceptible to being formed in the above manner.

FIG. 3 illustrates one particular use for the contact 10 in a typicalconnector setting. More specifically, a first electronic device 50 isprovided and can be in the form of an conventional connector or printedcircuit board (PCB), as illustrated. The exemplary PCB 50 has a firstface 52 and an opposing second face 54 and includes at least one bore 56formed therethrough for receiving the pin 20. The bore 56 is thereforecomplementary in shape as the shape of the pin 20 so that the pin 20 iseasily received within the bore 56. Preferably, there is a slight gap orspace between the pin 20 and the walls defining the bore 56 so that acoupling material 51, such as solder, is received therein around the pin20 to produce a secure electrically conductive connection between thepin 20 and the PCB 50. In FIG. 3, this coupling material 51 is in theform of solder material at and near the pin second end 24 that producesa soldered connection between the pin 20 and the PCB 50.

Preferably, the thickness of the PCB 50 is such that the second end 24of the pin 20 does not or only slightly protrudes beyond the second face54 when the contact 10 is securely connected to the PCB 50 during agiven application. Of course, the second end 24 can extend a greaterdistance beyond the second face 54 in some certain applications.

The member 40 serves as a locating member since it limits the degree oftravel of the pin 20 within the bore 56 of the PCB 50 by beingpositioned adjacent the first face 52 of the PCB 50. In other words, themember 40 acts as a stop by abutting the first face 52 of the PCB 50 andtherefore, when the contact 10 is securely attached to the PCB 50, themember 40 sits flush against the first face 52.

The contact 10 can act as a connector by electrically connecting thefirst electronic device (PCB 50) to a second electronic device 60 whichcan be in the form of a connector or another PCB. In the illustratedembodiment, the second electronic device 60 is a second PCB that iselectrically connected to the first PCB 50. The second PCB 60 includes afirst face 62 and a second face 64 that faces the first face 52 of thefirst PCB 50. Instead of being of the type that has through bores formedtherethrough, the second PCB 60 is of the type that has at least one andpreferably a plurality of conductive pads 66 formed along the secondface 64 and for electrical connection to the pin 20 of the contact 10.More specifically, the pin 20 is electrically connected to theconductive pad 66 by means of the heat re-flowable material 30.

The first end 22 is first positioned relative to the conductive pad 66so that the heat re-flowable material 30 is disposed near or adjacentthe conductive pad 66. Heat is applied to the PCB assembly as byconventional techniques (e.g., hot air, oven, etc.) so as to cause thematerial 30 to re-flow as illustrated in FIG. 3. As the material 30re-flows, the material contacts and flows across the conductive pad 66and when the material 30 cools, a secure soldered connection is formedbetween the conductive pad 66 and the first end 22 of the pin 20. Sincethe connection between the second end 24 and the first PCB 50 is of anelectrically conductive type, the pin 20 serves to electrically connectthe first PCB 50 to the second PCB 60. Accordingly, the contact 10 isthrough whole mounted relative to the first PCB 50 and is surfacemounted relative to the second PCB 60.

It will be appreciated that this application illustrated in FIG. 3demonstrates two parallel PCBs 50, 60 being interconnected by at leastone and preferably a plurality of discrete laterally-spaced pinnedsolder balls (only one of which is illustrated). It is understood thatthe components mounted to the PCBs 50, 60 are not shown, but in a powersupply application, typically, the upper PCB 50 is populated on bothsides with electronic components. The second end 24 of the pin is seatedwithin the bore 56, which can be a metallized via or plated through holeof the PCB 50.

One of the advantages of the present contact 10 is that the member 40 isformed of a conductive material, such as aluminum, as opposed to aninsulator and furthermore, the member 40 has heat dissipating properties(unlike an insulator) and therefore the heat collecting disadvantagesassociated with conventional connectors are avoided. More specifically,the member 40 serves as a thermal dissipater and therefore heat iseffectively wicked away from the first PCB 50 at an interface betweenthe first PCB 50 and the member 40. Because the interface between thefirst pin end 22 and the first PCB 50 is of an electrically conductivenature, heat is generated during normal operation conditions. One willappreciate that the heat is generated at locations underneath thelocator member 40 and since the locator member 40 seats flush againstthe first face 52, the locator member 40 acts to trap the heatunderneath the member 40 and within the first PCB 50. This results inheat buildup and can lead to malfunction and/or damage to the first PCB50. By placing a heat dissipating material near the interface connectionbetween the contact 10 and the first PCB 50, heat is effectivelydissipated through the member 40 away from the first PCB 50.

FIG. 4 illustrates yet another embodiment in which a contact 70 isprovided and is adapted for surface mounting to a conductive pad (suchas conductive pad 66 of FIG. 3) on the underside of an upper PCB 50. Thecontact 70 uses a shorter electrically conductive pin 72 that has a headportion 74 and a conductive locator member 76 is provided and surroundsthe pin 72 as in the earlier embodiment. Preferably, the dimensions ofthe head portion 74 are about equal to the dimensions of the locatormember 76 such that outer edges thereof are substantially axiallyaligned with one another. The heat re-flowable material 30 is disposedand retained at the free end 75 of the pin 72. The pin terminates at thehead portion 74 so that the head portion 74 can act as a conductive padthat can be surface mounted and soldered to the respective conductivepad that is part of the PCB. The locator member 76 can be in the sameform as the member 40 illustrated in FIG. 2 in that it can be acylindrical collar that surrounds the pin that extends therethrough.

FIG. 5 illustrates yet another embodiment of a contact 80 which issimilar to the contact 70 of FIG. 4 except for the below differences. Inthe contact 80, the dimensions of a locator member 82 do not necessarilyhave to match the dimensions of a head portion 84 of a pin 83. In theillustrated embodiment, the dimensions of the locator member 82 are lessthan the dimensions of the head portion 84 and thus the head portion 84extends beyond the locator member 82. The head 84 is formed with aplurality of outwardly opening radially extending channels 86 in itsupper surface. The upper surface of the channeled head 84 provides theprincipal contact with the conductive pad formed on the underside of theupper PCB. The channels preferably are formed so that they extend to theends of the head 84 and are open thereat so as to permit out-gassing ofvaporized solder flux. The formation of channels minimizes skating andhelps self-centering of the pin to the pad during solder re-flow andalso improves solder-joint strength.

FIG. 6 illustrates a cylindrical pre-formed washer-like solder element90 that can be formed on or otherwise disposed on (e.g., press fit) onone free end of the contact pin. FIG. 7 illustrates a square pre-formedwasher-like solder element 92. As with the material 30 in the form of asolder ball, the elements 90, 92 can be spaced from the locator memberor they can make slight contact therewith.

In yet another aspect of the present invention, a method of forming asolder ball at the end of the electrically conductive pin of the contactis provided. FIG. 8 is a cross-sectional view of a locator member 100according to another embodiment and includes a feature that facilitatesthe formation of a solder ball at the end of the electrically conductivepin. More specifically, the locator member 100 includes a first face 102and an opposing second face 104. For purposes of illustration only, thelocator member 100 is generally shown as a cylindrical collar; however,it will be appreciated that it can be in any number of different shapes.The locator member 100 has an opening or bore 106 formed therethrough toreceive the electrically conductive pin of the contact. In thisembodiment, the first face 102 has a recessed section 110 formed thereinwith the recessed section 110 being located about the bore 106. In otherwords, the bore 106 opens up into the recessed section 110. The recessedsection 110 is generally dish-shaped and therefore is characterized asbeing a concave surface formed in the first face 102. Preferably, thebore 106 is centrally located within the recessed section 110 which isannular in shape.

The concave recessed section 110 actually facilitates the formation of asolder ball at the free end of the contact pin in the following manner.Molten solder 30 is introduced to the first face 102 of the locatormember 100 as shown in FIG. 9 and the presence of the recessed sectionand the surface tension generated thereby between the non-wettablerecessed area 110 and the solder material 30 causes the molten solder toform a solder ball above the recessed section 110 as shown in FIG. 10.Since the contact pin extends through the bore 106 and therefore extendsabove the recessed section 110, the solder ball forms around the contactpin. The result is that the contact pin is embedded in the solder balland when the heat re-flowable material cools, the solder ball issecurely connected to the contact pin.

In this manner, the heat re-flowable material does not have to bepre-formed prior to use with the contact and instead, molten materialcan be injected onto the face 112 about the contact pin to form a solderball on the end of the contact pin. This permits the process to beautomated and the contacts can be formed more easily since it requiresless steps due to the elimination of the step of pre-forming the soldermaterial and since an injector can be used to simply and effectivelyintroduce an amount of solder material on the first face 102.

It will be appreciated that the locator member 110 according to thisembodiment can be used as a part of any one of the contacts disclosed inthe various present embodiments.

While exemplary drawings and specific embodiments of the presentinvention have been described and illustrated, it is to be understoodthat the scope of the present invention is not to be limited to theparticular embodiments discussed. Thus, the embodiments shall beregarded as illustrative rather than restrictive, and it should beunderstood that variations may be made in those embodiments by workersskilled in the art without departing from the scope of the presentinvention as set forth in the claims that follow, and equivalentsthereof. In addition, the features of the different claims set forthbelow may be combined in various ways in further accordance with thepresent invention.

1. A surface mount contact for coupling to an electronic device comprising: a conductive pin having an elongated body including a first end and a second end; a heat re-flowable bonding member coupled to the first end; and a conductive locator member disposed around the conductive pin in a region of the conductive pin between the second end and the heat re-flowable bonding member, wherein the locator member is a collar that radially protrudes from the conductive pin, the locator member having a conductive surface and an opening through which the conductive pin extends such that an annular volume of space extending radially outward from the conductive pin and substantially free of material is defined between the conductive surface of the locator member and the bonding member.
 2. The contact of claim 1, wherein the locator member is formed of aluminum.
 3. The contact of claim 1, wherein the pin has a cross-sectional shape selected from the group consisting of a circle, square, triangle, and rectangle.
 4. The contact of claim 1, wherein the locator member is press-fitted around the pin.
 5. The contact of claim 1, wherein the pin is formed of a metal selected from the group consisting of copper, copper alloy, and stainless steel.
 6. The contact of claim 1, wherein the heat re-flowable bonding member is in the form of a solder ball, with the first end of the pin being embedded therein.
 7. The contact of claim 1, wherein the heat re-flowable bonding member is a pre-formed solder mass. 